On 13 May 2015, ISIL took advantage of the military's redeployment the day before to Idlib province, where ongoing fighting was taking place,[6] and launched a two-pronged offensive towards Palmyra and its military sites, including Station 3 and the large weapon depots.[23] The operation started on the outskirts of Al-Sukhnah, northeast of Palmyra.[24] The militants captured al-Thinayya checkpoint at the northern entrance to the town, after which they advanced into major parts of Al-Sukhnah, with fighting taking place at the main police station, the headquarters of the Ba'ath Party and the National Hospital. This caused a state of panic among civilians in Palmyra and raised concerns about the possibility of ISIL attacking the nearby archaeological monuments.[24] In the end, ISIL took control of Al-Sukhnah,[15] giving them control over a strategic highway linking Homs with the Deir ez-Zor Governorate to the northeast.[25]

After the capture of Al-Sukhnah, ISIL took all the Syrian Army posts between it and Palmyra.[12] Fighting took place near the government security center of Hajjana and the officers' housing east of Palmyra, with ISIL taking control of several checkpoints, after hitting them with missiles.[24] As they advanced to the outskirts of Palmyra, they seized all of the Amiriya area, north of the city,[23][24] or at least its northern part, and the Muktab Al-Dour checkpoint in the eastern outskirts.[15] ISIL also reportedly took a large government ammunition warehouse outside Palmyra, and was bombing a nearby government-controlled airport.[6] The militants attempted to breach the eastern sector of the T-4 airbase but were repelled.[15] According to a pro-government source, the Syrian Army later launched a counter-attack and recaptured Amiriya and the Muktab Al-Dour checkpoint. Before nightfall, the Syrian Army and the NDF launched a counterattack at Al-Sukhnah as well, and reportedly infiltrated ISIL positions at the southwestern corridor.[15] In the evening ISIL seized Burj al-Ishara, a strategic high point near the historic Palmyra Castle.[26] At the end of the day, ISIL was still in control of the Deir ez-Zor-Al-Sukhnah road, with the Syrian Army attempting to retake it.[15]

The first day of fighting left 70 Syrian Army and 40 ISIL fighters dead, including the offensive's top ISIL commander.[12] On 14 May, the Syrian Army shelled Burj al-Ishara,[26] while ISIL made an attempt to break into the city of Palmyra.[27] The jihadists managed to enter the neighbourhoods in the eastern outskirts of the city, but were expelled by government troops.[1][28][29] After re-securing once again the Muktab Al-Dour checkpoint, government forces reportedly advanced to the village of Al-Basateen, where the eastern frontline remained that night.[1] ISIL also targeted during the day the Tadmor Prison and the airport in an attempt to seize the airbase's major weapons depot.[30] Elsewhere, government troops took full control of the Al-Hayl Gas Field, killing 32 militants, after which they proceeded to take Al-Thathah, Al-Fawl, Al-Mujawar, Al-Hawa, and Al-Sina'a. According to a military source, ISIL was still positioned one kilometer from Amiriya, and was in control of al-Sukhnah, but the Syrian Army remained at the outskirts of the village.[1]

On 15 May, the Syrian Army dispatched reinforcements to Palmyra, while ISIL was 1 km (0.62 mi) from the Palmyra archeological site,[31] but pulled back from the eastern outskirts to about 2 km (1.2 mi)[32] where clashes were still erupting as the Syrian Army launched a counter-offensive.[33] ISIL once again captured the northern part of Amiriya, killing a number of civilians, before they were pushed out again by heavy air-strikes. Two more attacks were launched against the air-base, with both being repelled. During the night, ISIL shifted its focus to the ruins but were unable to infiltrate them. Before dusk, Syrian Army units continued their counterattack at al-Sukhnah, reaching the town's outskirts. Reinforcements from the special forces unit, "Suqur al-Sahara," arrived to reinforce government forces.[16]

On 16 May, ISIL fighters reached the ruins and captured parts of the historic citadel of Fakhr-al-Din al-Ma'ani as fighting continued.[34] Later, ISIL once again seized Amiriya[35] and continued its advance, taking the northern part of Palmyra after a massive attack.[36][37]

By the morning of the next day, the Syrian Army had pushed ISIL back from Palmyra, fully securing the city.[38] The Syrian Army also recaptured Palmyra castle[35][39] and reportedly, the strategic Radio and Television Communication Hill (Burj al-Ishara) as well.[35] Life in the town returned to normal with stores and businesses gradually reopening.[40]However, fighting continued to the north in Amiriya[38] and east of Palmyra, where ISIL captured the T-3 Pumping Station and al-Hayl gas field.[9][41]

On 19 May, the SAA and NDF recaptured Amiriya.[9] As the Army smashed its way into forward ISIL positions, they discovered piles of tactical vests, thermal missiles, stacks of Muslim prayer books in Russian (left by Chechen fighters) and enough ammunition for each rebel to carry 10,000 rounds.[17]

In addition to the fighting in and around Palmyra, clashes took place at the nearby Jazal oil field between 18 and 20 May, leaving 48 soldiers and 30 militants dead. 150 soldiers were also wounded.[8]

On 20 May, ISIL recaptured Amiriya,[42] and managed to advance into Palmyra, capturing a third of the city.[7] ISIL attacks on other sectors around the town were reportedly repelled.[42] The renewed ISIL push came after 600–800 militant reinforcements arrived.[4] Later that day, ISIL nearly seized full control of Palmyra, after government forces withdrew. Government troops were still in control of a prison in the east and the military intelligence headquarters in the west. In an attempt to conserve some of the city's history, hundreds of statues were moved to safe locations, except for the large monuments that could not be moved. Fears were raised over the safety of the ruins and the city's museum.[43] This rescue operation was led by the Dutch heritage expert René Teijgeler.[44] By the evening, all Syrian Armed Forces had withdrawn from the city to its outskirts,[4] and ISIL also captured the airbase.[5]

According to state TV, the Syrian Army evacuated the city's civilians during their retreat.[45] In contrast, residents reported that civilians were in fact not evacuated, and that SAA officers fled the city ahead of conscripts and militias, leaving them to fend for themselves.[46] The Syrian government later backtracked on the claim it had evacuated civilians after an increase in refugees from the city caused by the bombardment of the town.[13]

On 21 May, ISIL fighters entered the ruins.[47] Meanwhile, ISIL captured the at Tanf Border Crossing, which was the last government-held border crossing with Iraq.[10] On 22 May, the American-led coalition in Syria conducted one airstrike near Palmyra, which destroyed six ISIL anti-aircraft artillery systems, and an ISIL artillery piece.[48]

Between 23 and 24 May, ISIL captured the al-Sawana area and the Missile Battalion base on the Palmyra–Homs road, resulting in the capture of more than 22 pro-government fighters.[8][11] The next day, 25 May, ISIL attacked the village of Jazal, located in the Al-Sha’ar Mountains and near the government’s strategic power grids and gas fields that provide electricity and gas to the western part of the country. After four hours of fighting, the assault was repelled.[49]

On 26 May, the frontline had reportedly moved to Al-Furqlus, the Shaar mountains, Qurayteen, and the Tiyas Airbase.[50] On the next day, Syrian government forces advanced in the Jazal oil field region.[51]

In early July 2015, the Syrian military launched an offensive in an attempt to retake Palmyra,[52] advancing up to 5 kilometres (3.1 mi) from the city.[53][54] In March 2016, another offensive was launched to retake the historic city of Palmyra, and the Syrian Army regained control of the town on 27 March 2016.[55][56]

During the offensive, ISIL conducted numerous executions. On 14 May, ISIL executed 26 civilians in Amiriya and al-Sukhnah for "dealing with the regime", of whom 10 were beheaded. The following day, another 23 civilians were executed in Amiriya, nine of them children.[14][57]

On 22 May, various pro-opposition sources in the city reported ISIL had executed between 150 and up to 280 government loyalists and soldiers in the streets[21] and in the public square by a shot-to-the-head or beheading. The executions were part of a purge which ISIL initiated, after capturing Palmyra, where the jihadists were conducting door-to-door searches to find and kill all government supporters or fugitive soldiers.[58] The pro-opposition activist group the SOHR put the number of killed in the city at 168, with another 600 soldiers and civilians detained,[19][20] while state TV reported 400 people had been executed. The pro-government Al-Watan newspaper put the number of executed at 450 as of 25 May.[59] According to a SAA soldier, ISIL beheaded the 19-year-old daughter of a general.[46]

In early July 2015, ISIS released a graphic video showing 25 teenage members of that group executing by shooting in the head a similar number of adult male captives dressed in dark fatigues and kneeling in front of them on the Palmyra theatre's stage area.[60]

On 18 August 2015, ISIS beheaded a respected antiquarian, Khaled al-Asaad (aged 83), who had worked for over 50 years as head of antiquities in Palmyra and hung his body on a column in a main square of the historic site.[61][62]

Multiple analysts cited the ISIL victory at Palmyra as evidence of the Syrian government's strategic withdrawal to defend larger populations centers, with government control still accounting for about 50–60 percent of the population.[64] Purportedly, in the view of the Syrian government, the fall of Palmyra was a tactical defeat but a strategic gain, as the capture of the city and the UNESCO World Heritage site would potentially encourage the United States to review its Syria policy, make Jordan more aware of the threat from ISIL, and force Iraq to increase cooperation with Syria.[65]

Ayham Kamel, the Eurasia Group's Middle East & North Africa director, stated that the ISIL victory demonstrated that the Syrian government was no longer capable of maintaining nominal control in each of the provinces of Syria, and was possibly being forced to pick its battles.[63]

^ ab"ISIS purges Syria's Palmyra of Assad loyalists". The Times of India. AP. 23 May 2015. Archived from the original on 25 May 2015. Retrieved 23 May 2015. Hamza said the public killings in Palmyra appeared aimed at winning support of residents who opposed Assad's rule, and that the strategy was succeeding with some [...] "People don't seem to be resentful of the new guidelines. They are saying it is much better than the regime, which used to terrorize the whole town, especially through the arrest campaigns", Hamza said.